Palm vein authentication is biometric authentication technology by which the vein pattern of a palm is photographed by using near infrared rays so as to authenticate an individual on the basis of the vein pattern. When a vein pattern is registered, the posture of the hand, which is the subject, can be corrected by using a guide, whereas when matching is conducted for the vein pattern, a guide is often unavailable. In such a case, a posture difference in the hand between when it is used for registration and when it is used for matching results in a larger difference between the registered data and the matching data, decreasing the success rate in authenticating the person who is eligible to be authenticated.
In view of this, it is conceivable to measure the posture of a hand such as the inclination, the rotation, etc. of the palm so as to correct the image of the palm photographed for the matching in such a manner that the posture difference in the hand between the registration and the matching are cancelled. Normalizing images by using this method increases the success rate in authenticating the person who is eligible to be authenticated.
Shape From Shading (SFS) technology is also known in which the three-dimensional shape of a subject is estimated on the basis of the brightness distribution in a subject image picked up with illumination light cast on the subject (For example, non Patent Documents 1 through 3).
A fundamental pattern mapping method is also known in which a two-dimensional texture with a fundamental pattern is mapped on an adjustable curved surface made of a three-dimensional curved surface so as to create repeatedly a fundamental pattern on the adjustable curved surface (For example, Patent Document 1).    Patent Document 1: Japanese Laid-open Patent Publication No. 04-96186    Non Patent Document 1: R. Kimmel et al., “Global Shape from Shading”, CVGIP: Image Understanding, pp. 120-125, 1994    Non Patent Document 2: R. Zhang et al., “Shape from Shading: A Survey”, IEEE PAMI (Transactions on Pattern Analysis and Machine Intelligence), Vol. 21, No. 8, pp. 690-706, August 1999    Non Patent Document 3: E. Prados et al., “Shape from Shading: a well-posed problem?”, INRIA, No. 5297, pp. 1-55, August 2004